Fix wxGTK compilation when using non X11-based GDK.

Only use X11-specific GDK functions inside "#ifdef GDK_WINDOWING_X11" checks.

Closes #14044.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70701 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/utilsgtk.cpp

@@ -27,7 +27,12 @@
 #include "wx/evtloop.h"
 
 #include <gtk/gtk.h>
+#ifdef GDK_WINDOWING_WIN32
+#include <gdk/gdkwin32.h>
+#endif
+#ifdef GDK_WINDOWING_X11
 #include <gdk/gdkx.h>
+#endif
 
 #if wxDEBUG_LEVEL
     #include "wx/gtk/assertdlg_gtk.h"